Handbook on Basic Principles of Textile Processing

Dedication

This article is dedicated to the cherished memory of my professor, the late C. B. Gupta, whose wisdom, guidance, and passion for textile processing have been a lifelong source of inspiration. His unwavering dedication to knowledge and excellence continues to shape my understanding and appreciation of this field. I am forever grateful for his teachings and the invaluable lessons he imparted.

Foreword

The manufacturing of textiles is one of the oldest and most vital global industries. The study of textiles begins with fibers, the foundational raw materials that are converted into yarn, knitted or woven into fabric, and ultimately fashioned into garments.

This handbook provides a comprehensive outline of the processing techniques for knitted fabrics made from cellulosic fibers. It is written for professionals, students, and anyone in the textile trade seeking a solid foundational background to support their work. Every effort has been made to ensure that the text is accurate, technical, and up to date.

Introduction

Knitted fabric processing plays a crucial role in the textile industry, ensuring quality, durability, and aesthetic appeal. This handbook outlines the essential principles and techniques involved in the processing of knitted fabrics, spanning from raw material selection to final finishing treatments.

Chapter 1: Understanding Knitted Fabrics

What is Knitting?

Knitting is a fabrication method where yarn is manipulated to create a textile by interlooping rows of stitches. It can be performed by hand or by machine. The process involves using needles to interlink a series of loops formed from one or more continuous threads. Each loop connects to the preceding one, creating a flexible, cohesive structure.

1.1 Types of Knitted Fabrics

• Weft Knitting: Loops are formed horizontally across the width of the fabric. It is broadly categorized into two types:

  • Single Jersey: Knitted on a machine equipped only with a cylinder. Examples include standard Single Jersey, Pique, 2-Thread French Terry, 3-Thread Fleece, Sherpa, and Twill.

  • Double Jersey: Knitted on a machine featuring both a cylinder and a dial positioned at 90° to each other, allowing needles to operate on both components. Examples include 1x1 Rib, 2x2 Rib, Interlock, Ponta de Roma, Milano Rib, Variegated Rib, and Flat Back Rib.

• Warp Knitting: A method where loops are formed vertically along the length of the fabric from separate warp yarns. Common examples include Tricot, Raschel, and Milanese knits.

1.2 Properties of Knitted Fabrics

• High elasticity and stretchability

• Excellent air permeability and moisture management

• Superior wrinkle resistance

• Comfortable drape and form-fitting characteristics

1.3 Technical Terminology of Knitted Fabrics

• Count: The linear density or thickness specification for spun yarn.

• Denier: The weight in grams of 9,000 meters of filament yarn, indicating its yarn count.

• Dia: The diameter of the knitting machine cylinder.

• GG (Gauge): The number of needles per inch on a knitting machine, indicating fabric fineness.

• Needles: Hooked wire components used to form loops in the fabric.

• Sinker: A thin metal plate used to support loop formation and holding down fabrics in single jersey machines.

• All Feeder: A configuration where a specific yarn (such as elastane/spandex) is introduced into every yarn feeder during plaiting.

• Alternate Feeder: A configuration where plaited yarn is introduced into every second (alternate) feeder.

• Tubular Fabric: Fabric knitted in a seamless, cylindrical shape.

• Open Width Fabric: Fabric that is either slit during the knitting process or post-knitting to lay flat.

• Flat Knit: Fabric knitted directly in a flat, open-width form without requiring slitting.

• Circular Knit: Fabric produced in a seamless tube on a cylindrical machine. Modern circular machines can optionally slit the fabric directly on the machine.

• TPI (Twists Per Inch): The number of turns per inch in a yarn. Knitted yarns typically require a lower TPI than woven yarns to retain softness.

• Loop Length: The linear length of yarn required to form one complete knitted loop.

• GSM (Grams per Square Meter): The standard metric weight used to measure the density, thickness, and substance of a fabric.

Chapter 2: Pre-Treatment Processes

Pre-treatment involves preparing the greige fabric for subsequent coloration processes by removing natural and added impurities. While several steps are detailed below, the exact sequence depends entirely on the desired properties of the final product.

What are impurities in cotton fiber?Cotton fibers naturally contain organic impurities like proteins, pectins, waxes, and natural coloring matters. Additionally, temporary impurities such as spinning oils, knitting lubricants, greases, and sizing agents are added during manufacturing and must be removed.

2.1 Singeing

Singeing is a finishing process that burns off protruding, loose fiber ends from the fabric surface using a controlled flame. This treatment dramatically improves fabric appearance, minimizes pilling, and produces a smoother face for uniform dyeing or printing. While traditionally used for woven goods, tubular or open-width singeing machines are increasingly utilized in high-end knit processing to achieve eco-friendly brightness and smoothness.

2.2 Scouring

Scouring is a vital chemical pre-treatment that removes waxes, oils, and pectins. By treating the fabric with alkaline solutions (such as caustic soda), detergents, or specialized enzymes, the fabric becomes highly hydrophilic (absorbent). This is a prerequisite for level and consistent dye uptake.

2.3 Mercerizing

Mercerization is a chemical treatment for cellulosic fibers like cotton, performed by exposing the fabric to a concentrated solution of sodium hydroxide ($\text{NaOH}$) under high mechanical tension. This process swells the cell wall, increasing fiber tensile strength, chemical reactivity, dye affinity, luster, and structural smoothness.

2.4 Biopolishing (Enzyme Treatment)

Biopolishing utilizes cellulase enzymes to cleanly remove loose, fuzzy micro-fibers from the fabric surface. It can be executed before, during, or after the dyeing cycle.

Technical Recommendation: > While executing biopolishing during the dyeing cycle is highly popular for efficiency, it poses a significant risk of creating permanent "rope marks" on heavyweight or stretch fabrics—particularly in dark shades like Brown, Green, and Royal Blue.In dark shades, large turquoise-based dye molecules can cause foam buildup within the fabric ropes. Entrapped loose lint aggravates this friction, creating localized pale streaks. Therefore, for heavy or stretch fabrics in dark shades, I strongly recommend performing biopolishing after the dyeing stage as a safe, defect-free method.

2.5 Terminology Used in Pre-Treatment

• Loading: The process of feeding and threading the greige fabric into the processing vessel.

• Absorbency: A measure of the fabric's hydrophilicity, evaluated by tracking the absorption time of a water droplet.

• pH: The measure of acidity or alkalinity. Tested via pH paper or digital meters: orange-to-red indicates acidic conditions, while green-to-blue indicates alkaline states.

• Wicking: The height to which water rises vertically through a fabric strip via capillary action.

• Whiteness Index: A colorimetric evaluation indicating the baseline whiteness of a fabric, proving the effective extraction of natural pigments.

Chapter 3: Dyeing and Printing

Coloration adds aesthetic and commercial value to the textile. Based on the delivery method of the colorant, it is classified as either dyed or printed.

• Dyeing: The uniform application of colorants to fibers, yarns, or fabrics in a vessel under specific pH, temperature, and electrolyte conditions to achieve exhaustion and chemical fixation.

• Printing: The localized application of colorants in precise, repeating geometric or artistic patterns using thickeners to restrict color migration.

3.1 Dyeing Methods

Coloration requires a thermodynamic or mechanical driving force to diffuse dye molecules into the fiber matrix. Based on this mechanism, dyeing is split into two major methodologies:

Method	Process Type	Mechanism
Exhaust Dyeing	Batch Process	Dyes are progressively shifted ("exhausted") from the liquor into the fiber via chemical affinity, regulated temperature gradients, and salt/alkali fixation over a 30 to 60-minute cycle.
Pad Dyeing	Continuous / Semi-Continuous	Fabric passes through a concentrated dye bath and is squeezed through heavy rollers for uniform distribution. In Cold Pad Batch (CPB), fabric is batched on rollers for 8 hours to fix colors at room temperature. Alternatively, rapid continuous lines use immediate steaming units to accelerate fixation.

3.2 Printing Techniques

Printing techniques are classified by the chemical style of application and the physical machinery setup.

Styles of Printing:

• Direct Printing: Applying dye or pigment paste directly onto a white or light-colored ground.

• Resist Printing: Printing a protective paste onto fabric that prevents dye penetration during subsequent immersion dyeing.

• Discharge Printing: Printing a chemical reducing agent onto a pre-dyed background to selectively destroy and remove the base color, leaving a white or newly colored pattern.

Methods of Print Application:

• Block Printing

• Flatbed Screen Printing

• Rotary Screen Printing

• Digital Inkjet Printing

• Engraved Roller Printing

• Stencil Printing

• Flexographic Printing

• Heat Transfer (Sublimation) Printing

Chapter 4: Finishing Treatments

Finishing represents the final production phase designed to make the fabric commercially viable and consumer-ready. It alters the hand, appearance, drape, stiffness, and dimensional stability according to client specifications. Finishes are divided into mechanical and chemical pathways.

4.1 Mechanical Finishing (Physical Adjustments)

These processes rely exclusively on moisture, pressure, tension, and temperature to alter the fabric structure.

• Steaming: The premier medium to relax stresses within knit loops and establish initial fabric stability.

• Calendering: Passing fabric through heated, pressurized rollers to flatten it and impart surface luster.

• Sueding / Peaching: Using abrasive rollers to gently scratch surface fibers, creating a soft, napped skin feel reminiscent of a peach.

• Raising / Brushing: Pulling up fiber ends from the yarn structure to create a fuzzy, insulating surface nap (e.g., fleece).

• Compacting: A mechanical process that pre-shrinks knitted fabrics lengthwise to minimize residual shrinkage after consumer washing.

4.2 Chemical Finishing (Functional Additions)

These treatments involve applying specialized chemical formulations to add functional or tactile properties.

• Silicon Softeners: Imparts an ultra-smooth, slick, and premium soft hand feel.

• Water Repellent: Modifies surface energy to make the fabric hydrophobic, resisting water penetration.

• Stain Repellent: Prevents oil- and water-based stains from adhering to the fibers.

• Wicking Finish: Accelerates moisture transport away from the skin for activewear applications.

• Anti-Pilling Finish: Restricts fiber migration to prevent fuzzy ball formation on the fabric face.

• Anti-Curling Finish: Stabilizes the edges of single jersey fabrics to prevent rolling during garment cutting.

• Antimicrobial Finish: Inhibits bacterial growth to eliminate odors and improve hygiene.

• UV Protection Finish: Absorbs or reflects harmful ultraviolet rays to protect the wearer.

• Aloe Vera Finish: Infuses cosmetic micro-capsules for skin-nourishing benefits.

• Malodor Absorbent Finish: Chemically traps environmental odors to keep garments smelling fresh.

Chapter 5: Quality Control and Testing

Because textile processing involves highly sensitive chemical reactions and physical stress variations, rigorous quality control is critical to guarantee consistency and meet international trade expectations.

5.1 Key Quality Parameters

• Color Fastness:

  • Fastness to Washing (Color fading or bleeding during home laundering).

  • Fastness to Water (Color migration when wet).

  • Fastness to Rubbing/Crocking (Dry and Wet mechanical rub transfer).

  • Fastness to Perspiration (Acidic and Alkaline body sweat interactions).

  • Fastness to Light (Degradation and fading from UV light exposure).

  • Fastness to Bleach (Resistance to chlorine and non-chlorine oxidizers).

  • Fastness to Saliva (Critical evaluation for infant wear safety).

  • Fastness to Dry Cleaning.

• Dimensional Stability (Shrinkage): Measuring changes in length and width directions after standardized washing and drying cycles. Testing is typically performed after 1 wash and validated up to 3 washes.

• Appearance After Washing: Inspecting for twisting, torqueing, seam skewing, or fuzziness post-wash.

• Bursting Strength: Evaluating the multi-directional pressure resistance of the knit network (measured instead of tensile strength due to the looped nature of knits).

• Sewability: Ensuring the fabric can be stitched without needle cutting, yarn severing, or seam puckering.

• GSM (Mass per Unit Area): Ensuring compliance with specified commercial fabric weights.

• Blend Percentage: Quantitative verification of fiber ratios (e.g., 60% Cotton / 40% Polyester).

• Pilling Resistance: Mechanical tumbler testing to verify resistance to surface fuzzing.

• pH Testing: Confirming the fabric surface is neutral to avoid skin irritation.

5.2 Standard Testing Methods

To ensure data is globally reproducible, testing must occur within a strictly climate-controlled laboratory setting ($20^\circ\text{C} \pm 2^\circ\text{C}$ and $65\% \pm 4\%$ Relative Humidity) using standardized procedures established by international agencies:

• AATCC: American Association of Textile Chemists and Colorists

• ASTM: American Society for Testing and Materials

• ISO: International Organization for Standardization

• JIS: Japanese Industrial Standards

• BS: British Standards

• M&S Standards: Proprietary retailer testing protocols (Marks & Spencer)

Conclusion

The textile processing of knitted fabrics is an intricate, highly technical sequence of operations. Successfully managing each stage—from pre-treatment through coloration to final finishing—ensures production efficiency, manufacturing sustainability, and final product excellence.

To expand on these core principles, detailed standalone handbooks covering each individual processing stage will be released sequentially in upcoming editions of this series.